Most motor vehicles are supplied with one or more keys which are required to open and operate the vehicle. Whilst early motor vehicles relied upon a mechanical key, many modern keys are fitted with transponders which can communicate with the vehicle in order to provide additional security.
Transponder keys contain an electronic circuit having a non-volatile memory and at least one electrical winding. The keys are typically passive in that they require no battery or external electrical supply, and instead receive power by way of the electromagnetic vehicle signal emitted wirelessly from the vehicle which causes a current to flow in the electrical winding. Sufficient power is obtained to allow the electronic circuit to recognise the vehicle signal and to generate a response signal (which is also emitted wirelessly).
The response signal includes an identifier which can in turn be interpreted by the vehicle, the vehicle control system being activated, and thereby allowing the vehicle to be operated, if the identifier indicates that the correct key is present.
Many motor vehicle transponder keys are “magnetic coupled transponders”. These transponders operate at a frequency of 125 kHz or 134 kHz.
The vehicle is fitted with an antenna in the form of one or more induction coils which issue the vehicle signal to the key. For example, the vehicle signal may be issued as soon as the vehicle's doors are opened, or may be issued when the key is inserted and rotated in the ignition lock.
Some transponder keys have a very limited range, for example 50 mm. Such transponder keys cooperate with a vehicle antenna in the form of an induction coil located around the ignition lock, so that the antenna is less than 50 mm away from the handle of a key inserted into the lock.
In one known arrangement utilising such a transponder key, the key is inserted into the ignition lock and rotated to the ‘on’ position. The first stage of security is therefore provided by the mechanical form of the key, the mechanical form being required to match the form of the pins and tumblers within the ignition lock.
Turning the key to the ‘on’ position triggers the vehicle to emit the vehicle signal by way of its antenna. The winding in the handle of the transponder key absorbs some of the emitted energy and uses that energy to power the transponder's electronic circuit. The transponder emits its own response signal including the unique identifier. The response signal emitted by the transponder is usually digital and is received by the vehicle's antenna. The vehicle's security system interprets the response signal and if the identifier identifies the correct key the vehicle's operating system is activated and the vehicle can be operated. If the response signal does not include the correct identifier the vehicle's operating system is not activated and the vehicle cannot be operated. The transponder therefore provides a second stage of security, over and above the mechanical key.
Other transponders have a greater range and are used in vehicles having “keyless” operation. Such vehicles avoid the requirement for a mechanical key to be rotated in the ignition lock and rely totally upon the security provided by the transponder. Thus, the vehicle is typically fitted with several antennas which issue the vehicle signal, for example after the vehicle doors have been opened. Provided the transponder key is located within the vehicle (or very close to the vehicle) the transponder will receive sufficient power to energise the electronic circuit and issue a response signal. If the response signal indicates that the correct key is present the vehicle's operating systems are activated. Notwithstanding that a mechanical key is not required to operate such a vehicle, most vehicle manufacturers will nevertheless include a mechanical key to allow access to the vehicle in the event of a power failure.
A problem arises if the vehicle owner loses a transponder key, or both transponder keys in those cases where two transponder keys are supplied with the vehicle. It is necessary to supply a replacement or non-original transponder key having the correct mechanical form and the correct identifier.
It is possible to cut a key blank to the correct mechanical form, and there are many providers of key-cutting services. The key-cutter must choose the appropriate blank before cutting the mechanical form, but an appropriate blank can readily be identified, either visually or by way of the vehicle make and model.
It is also possible to program a replacement transponder key with the correct identifier for the vehicle, and vehicle suppliers and specialist operators such as the Automobile Association (in the UK) have the necessary equipment to program a replacement transponder key.
Notwithstanding that most of the motor vehicle transponder keys are magnetic coupled transponders operating at 125 kHz or 134 kHz, different transponder manufacturers utilise different operating parameters. Also, the transponder manufacturers update their operating parameters from time to time in line with developments in the technology and the desire to regularly improve security. Accordingly, not all transponder keys are compatible with all motor vehicles, and if an incompatible key is programmed with the correct identifier it will still not be able to be used because its response signal will not match the operating parameters required by the vehicle.
In those vehicles requiring the insertion and rotation of the mechanical key, it is necessary to cut the mechanical form of the key before the transponder can be tested. This can represent a significant problem for those operators offering the service of replacing transponder keys, since the cost of the replacement transponder key is significant and the replacement key will be wasted if the mechanical form has been cut and the key is subsequently found to be incompatible with the vehicle.
Since the transponder operating parameters will often be updated with each model change of a vehicle, and perhaps also at each design update for the vehicle, it is essential that operators providing replacement transponder keys are aware of every change of parameter for every type of transponder and every motor vehicle. In theory therefore, it is possible to ensure that only the correct type of replacement transponder key is sought to be programmed.
In practice, however, less diligent operators may not keep their records fully up to date and/or may not consult their records appropriately. Also, even the most diligent operator may not be able to identify whether a particular vehicle was manufactured before or after a relevant design update. In these cases, the operator might inadvertently seek to use an incompatible replacement transponder key.
There is a significant cost penalty in using an incompatible replacement transponder key. As above indicated the replacement key might be wasted if the mechanical form is cut before the transponder can be tested for compatibility with the vehicle. Even for those vehicles not requiring the insertion and rotation of a mechanical key, however, the operator may spend up to 30 minutes programming a transponder key, which time will be wasted if the transponder key is incompatible with the vehicle. Also, the operator typically has to pay a license fee for each transponder key he or she programs, so the programming of an incompatible transponder key has a direct financial penalty which cannot be recovered from the customer.